A heavy goods vehicle tire comprises a crown part surmounted radially on the outside by a tread intended to come into contact with the roadway, this crown part being extended on each side by sidewalls ending in beads. A tire comprises a plurality of reinforcement armatures including, in particular, a carcass reinforcement the purpose of which is to withstand the loads created by the tire internal inflation pressure. This carcass reinforcement extends into the crown, the sidewalls of the tire and is anchored at its ends to appropriate anchoring structures located in the beads. The carcass reinforcement is generally made up of a plurality of reinforcing members arranged parallel to one another and making an angle of or in the region of 90 degrees with the circumferential direction (in which case, the carcass reinforcement is said to be “radial”). The carcass reinforcement is usually anchored by turning it up around an anchoring structure of appropriate circumferential rigidity in order axially on the outside to form a turned-up portion of which the length, measured for example with respect to the radially innermost point of the anchoring structure, is chosen to provide the tire with satisfactory durability during use. Axially between the turned-up portion and the carcass reinforcement there are one or more elastomer-based materials which provide a mechanical coupling between the two parts of the carcass reinforcement.
In use, this tire is mounted on a mounting rim comprising rim seats intended to be in contact with the radially innermost parts of the beads and, axially on the outside of each seat, a rim flange intended to fix the axial position of the said bead when the tire is fitted and inflated to its nominal pressure.
In order to withstand the mechanical stresses of running, it is known practice to provide additional reinforcements that reinforce the bead, in the form in particular of plies arranged against at least a part of the turned-up portion of the carcass reinforcement.
During running, the tire beads are subjected to a great many bending cycles, thereby winding themselves around the rim flanges (that is to say partially adopting the geometry of the said flanges). This bending results in greater or lesser variants in curvature combined with variations in tension in the reinforcement armatures that reinforce the beads and, in particular, in the turned-up portion of the carcass reinforcement and in the said reinforcement. These same cycles induce compressive and extensile loadings in the materials of which the beads are made. Under running conditions, it is also found that the reinforcing members of the reinforcement of the carcass ply shift circumferentially and cyclically in the sidewalls and the beads of the tire. A cyclic circumferential shift is to be understood here to mean that the shift is in one direction and in the opposite direction each time the wheel revolves about a mean position of equilibrium.
Running generates within the materials of which the bead is made, and in particular within the elastomeric materials and most especially in those situated in the immediate vicinity of the ends of the reinforcements (the end of the turned-up portion of the carcass reinforcement or the ends of the additional reinforcements) stresses and/or deformations which may lead to a more or less appreciable reduction in the service life of the tire.
This is because these stresses and/or deformations may cause delamination and cracking near the ends of the said reinforcements. Because of the radial direction of the reinforcing members and because of the nature of the said reinforcing members (these are generally metal cables) of which it is made, the turned-up end of the carcass reinforcement is particularly sensitive to this phenomenon.
The document published under the reference WO 2006/013201-A1 describes a tire bead structure in which the carcass reinforcement has been not turned up by being wound partially over a bead wire but wound around an anchoring structure over at least one full turn in each of the beads. In this way, the end of the carcass reinforcement lies in a region of the bead which is not subjected to high cyclic stresses; it is thus possible to improve the endurance of the beads.
However, while such a tire bead structure is effective from a mechanical standpoint, it is nonetheless still expensive and tricky to implement using conventional industrial scale and manufacturing means.